webberweather
Gov't meteorologist. UNCC & NCSU Alum. Specializes in Climate Dynamics & S2S variability. Opinions are my own & not a reflection of my employer.
webberweather.com
- How do our low-level zonal wind anomalies over the Indo-Pacific the past few months compare to the onset years of every El Niño since 1950? Almost a perfect match overall. The westerly low-level wind anomalies deep in the Warm Pool are doing a lot of damage already to our current La Nina state
- Westerly wind anomalies deep into the Indo-Pacific during the fall before El Niño play a *very* underrated role in preconditioning/charging the Warm Pool over the West Pac The build-up of the West Pac Warm Pool provides the “fuel” for El Niño to grow later in the yr This yr is a classic example👇
- The mean Indo-Pacific Warm Pool last month looks similar to what preceded the 1982, 1997, 2006, 2014, & 2018 El Ninos The Warm Pool is plenty strong enough for El Niño later this year Note that 30C SSTs are centered ~160E & extend to nearly the dateline below the equator
- Euro weekly 7-day avg precip anomaly fcst for mid Jan (left) vs correlation b/t the CPC’s EP/NH index & OLRa (right) Note the Eq. Rossby Wave ~150-160E in the Eq. Pacific in both images, where 2 anomalous centers of convective heating straddle the equator. That’s usually how you get -EPO in winter
- NDJF N Pacific SLPa 1 year before El Nino (left) vs the Euro weekly forecast thru early Jan (right) This year has a classic negative N Pacific Oscillation (-NPO) pattern that often precedes El Nino events in the following calendar year See Vimont et al (2003): journals.ametsoc.org/view/journal...
- Rather unsurprisingly, the easterly trade winds are MIA relatively speaking as this -NPO pattern strengthens its grip on the North Pacific
- The ongoing MJO event in the West Pacific has led to a *gigantic* build-up of westerly momentum in the tropical troposphere, w/ GLAAM anomalies approaching 3 sigma! Very El Nino-like
- TAO buoy subsurface animation for this past month Notice the thermocline is quickly deepening and the subsurface anomalies are beginning to advance eastward over the West-Central Equatorial Pacific.
- The thermocline in the West-Central Eq. Pacific is already responding to the Westerly Wind Burst event & -IOD collapse that occurred earlier this month in association w/ the MJO. A downwelling Kelvin Wave is forming over the West Pacific & will help eventually destroy La Nina in a few months or so.
- We likely won't realize the true scope of the ocean response to this MJO event until early Jan or so, but early signs already point to a pretty big ocean response, even before the WWB event in the West-Central Pacific has occurred La Niña is living on borrowed time in the grand scheme of things
- Had to check myself into the ER last night with some nasty heart palpitations, felt like I was having a heart attack. 😣 Results came back negative fortunately & I feel better this morning w/ the occasional palpitation still Hopefully when I see the cardiologist they can diagnose the issue 🙏
- The GEFS and Euro AIFS ensembles trying to give me some hope for snow in early December. Surely, this must be a trap.
- It’s so hard to get things to work out in the Desert Lowlands of southern NM & El Paso, even if the longwave pattern is there for a good snow event. Oth, the pattern is close enough on some guidance to where it‘s legitimately possible (albeit rather unlikely) that they do.
- The low-level westerly wind burst in the pacific is what’s really driving the MJO into the Western Hemisphere (phase 8) in Dec (left) That to me is a very telling of how hard the atmosphere is pushing the ocean away from La Niña & possibly towards an El Niño state this coming spring or summer
- The warmest water on the entire planet is sitting ~160E in the Equatorial Pacific & a prolonged Westerly Wind Burst event is about to occur here This will trigger a downwelling oceanic kelvin wave that should destroy La Niña ~3 months from now & begin moving the ocean towards El Niño conditions
- We might be in a La Niña at the moment, but the tropical troposphere already looks very El Niño-like with a huge build-up of deep-layer westerly wind anomalies In the grand scheme of things, El Nino is likely knocking on the door 🚪
- For all my S2S junkies out there, here’s another invaluable tool to add to your arsenal: An annual archive of polar cap geopotential height anomalies going back to 1940 using ERA-5 & a 30-year sliding climatology 👀 hebweather.net/prod/gph_arc...
- Cool study came out earlier this yr looking at the dynamical origins of the extreme 2023 Heatwave in the Desert SW They concluded that the warm Tropical Atlantic was the primary culprit The partial regression analysis (left) & AGCM forcing (right) are pretty telling www.nature.com/articles/s41...
- I still can’t get over how similar this year’s zonal wind anomalies in the tropics are to 1981
- Quietly while La Niña persists, the tropical upper troposphere is becoming very El Niño-like A large build-up of westerly momentum (+U) in the tropics is being supplanted by a West Pac MJO orbit & repeated bouts of positive E Asia Mtn Torque (+EAMT) fluxing/squeezing +U equatorward
- This increase in tropical westerly momentum favors an equatorward shift in the Pacific Jet Stream, which leads to an increase chance of high-latitude North Pacific blocking (-EPO), consistent with current model forecasts & Winters et al (2019) journals.ametsoc.org/view/journal...
- The global tropics zonal wind anomalies this year are evolving very similarly to late 1981, which of course preceded a “Super” El Niño event in 1982 Note how this yr & 1981 have a big & slow westerly wind burst over the Indian Ocean & Maritime Continent in Oct-Nov that moved into the Pacific in Dec
- As you might expect from the very strong -IOD event strengthening La Nina’s footprint globally, this October’s observed pattern has deviated very little from the last 30 years worth of La Ninas over N America
- The latest Euro weekly forecast thru mid-December is almost exactly what you’d expect for typical a La Niña December over the last 30 years: A faster-than-usual start to winter over the East-Central US with plenty of high-latitude blocking
- Even when you look at November, this year really isn’t doing anything out of the ordinary for a La Niña
- La Niña is living on borrowed time. The extreme -IOD we're currently seeing (right) is about to collapse because the warm water in the Equatorial Indian Ocean will get flushed into the tropical West Pac at depth over the next month in this MJO event's westerly wind burst (left)
- This winter seems to be intent on following the cool ENSO/East QBO/solar max paradigm of early winter -AO/-NAO I replicated Gray et al (2004)'s analysis except used SLPa from 20CR & isolated -ENSO (left), which is close to the latest Euro weekly forecast (right) journals.ametsoc.org/view/journal...
- The other key takeaway here about these kinds of winters is that we see more frequent early winter -AO/-NAO & stratospheric warming events (as the latest Euro weeklies below suggest), followed by a much stronger polar vortex in mid-late winter (Jan-Feb)
- This early winter -AO, followed by significant +AO is also more believable given the favorable precursors we have in place for a -EPO/+TNH style pattern this year, which will likely grow only more prominent as the winter wears on due in large part to wave reflection
-
View full threadThis favors slower MJO events which have stronger & more consistent extratropical teleconnections as Yadav et al (2024), Yadav & Straus (2017) & Tseng et al (2020) have argued agupubs.onlinelibrary.wiley.com/doi/full/10.... journals.ametsoc.org/view/journal... journals.ametsoc.org/view/journal...
- Worth mentioning, this year has the 2 main precursors to a -EPO/+TNH ("polar vortex" pattern) dominated winter in place atm as identified by Zhong & Wu (2023). Namely, a warmer-than-normal Maritime Continent & West Pac as well as a Eurasian Snow Cover Dipole. journals.ametsoc.org/view/journal...
- Both of these lead to the development of this pattern, which often becomes more strong/persistent late winter as it interacts w/ the stratospheric polar vortex via wave reflection. Here's what this -EPO/+TNH or "ABNA" pattern looks like in winter (annotated over their fig 1)
